The simplest form of a contactless damper, such as a slinger or spray apparatus, is described in the referenced German Pat. No. 24 39 999. The disclosure of this patent describes a spray device by means of which damping liquid in form of drops or droplets is applied to a first roller having a hard surface. The surface is preferably metallic. It is also possible to apply damping liquids to such a surface by means of brushes, see for example Swiss Pat. No. 609,911. The damping liquid then is homogenized, for example by means of a rubbing roller, and applied by an application roller having a soft surface on the printing plate of a cylinder which is to have the damping liquid applied.
It has also been proposed--see U.S. Pat. No. 3,924,531, to which German Pat. No. 22 58 321 corresponds--to include an additional rubbing roller between the first roller receiving the damping liquid, that is, on which the damping liquid is sprayed or applied by brushes, and the actual damping liquid application roller applying the damping liquid on the plate of the plate cylinder. In accordance with the usual convention known and used in the inker and damper technology, this additional roller has a hard, usually metallic surface. Such a rubbing cylinder is, as known, driven by a positive drive; the actual damping application roller is carried along by friction. The intermediate rubbing or distribution or homogenizing cylinder usually is chrome-plated, that is, has a layer thereon which is hydrophilic, or otherwise, is receptive to damping liquid. The damping liquid application roller always must be soft, or elastic, at least at its surface, and for that reason it is usually supplied with an outside coating or jacket of rubber or plastic.
All roller coatings, known and customarily used in printing machinery, which apply damping liquid to the plate cylinder also, however, accept ink. The ink on the damping liquid application roller prevents formation of a closed and uniform layer of damping liquid, for example of water, since the liquid will adhere to this, usually undesirable, ink layer in form of drops or droplets, or will be worked into this ink layer in such form. This is particularly disadvantageous in the printing machines in which subsequent damping is used, that is, in which water or other damping liquid is applied to the printing plate to be damped after inking thereof. In this case, the ink application roller will not have a smoothing effect, and a non-uniform application of water will be directly visible on the printed subject matter. It is frequently possible to observe, on the printed copy, the formation of drops.
It has been proposed from time to time to cover the rubber coating of the ink application roller by a sleeve of textile or felted or felt-like material which, by storing damping liquid, or water therein, is intended to repel ink, and thus enhance the formation of a film of damping liquid on the printing plate. For this reason, it has been customary to place between the homogenizing or rubbing cylinder with the hard metallic surface and the plate cylinder carrying the plate only the damping liquid application roller, which is always required.